Three major problems which may be encountered with endocardial pacemaker electrodes during use are (1) a lack of stable position, (2) a chronic increase in stimulation threshold, and (3) a diminishing magnitude of the sensed endocardial signal. These problems are particularly manifested in the atrium, where maintenance of a stable anatomical position of the electrode has been a particularly difficult problem in the development of satisfactory endocardial leads for atrial pacing.
Another problem which is manifested in the blood stream by polished metal surfaces, such as are typically used in pacemaker electrodes, is the tendency to cause the formation of blood clots which may break loose and emobolize to various parts of the body.